Method of manufacturing perovskite powder, perovskite powder manufactured by the same and multilayer ceramic electronic component

ABSTRACT

There are provided a method of manufacturing perovskite powder, and perovskite powder and a multilayer ceramic electronic component manufactured thereof. The manufacturing method includes: washing metal oxide hydrate to remove impurities therefrom; adding pure water and an acid or a base to the metal oxide hydrate to prepare a metal oxide sol; mixing the metal oxide sol with a metal salt to form perovskite particle nuclei; and conducting grain growth of the perovskite particle nuclei by hydrothermal treatment to produce perovskite powder. The method of manufacturing perovskite powder and the perovskite powder manufactured by the same have advantages such as excellent crystallinity, reduced generation of fine powder, and favorable dispersion properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2010-0126242 filed on Dec. 10, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing perovskitepowder in the form of microparticles with excellent crystallinity andfavorable dispersion properties, by the preparation of a highconcentration and high purity metal oxide sol, as well as perovskitepowder and a multilayer ceramic electronic component manufactured by thesame.

2. Description of the Related Art

Perovskite powder is a ferroelectric ceramic material and broadly usedas a raw material of electronic components such as a multilayer chipcapacitor (MLCC), a ceramic filter, a piezoelectric device, aferroelectric memory, a thermistor, a varistor, and the like.

Since electronic component manufacturers have recently tended to produceelectronic components with decreased size and weight, increased capacityand improved reliability, ferroelectric particles are required to have arelatively small size, high dielectric constant and excellentreliability.

Conventional methods of manufacturing perovskite powder include a solidphase method and a wet process, and such a wet process includes oxalateprecipitation, hydrothermal synthesis, and the like.

The solid phase method typically has disadvantages such as producingpowder containing relatively large particles having a minimum particlesize of about 1 micrometer, difficulties in controlling particle size,agglomeration of particles, contamination during the firing ofparticles, and the like, therefore, the solid phase method entailsproblems in the production of perovskite powder with regard tomicroparticles thereof.

In a variety of conventional processes, the tetragonality of dielectricparticles generally deteriorates when the particle size thereofdecreases. If the particle size is reduced to less than 100 nm, it isvery difficult to secure a desired crystal axial ratio (c/a).

Further, with a decrease in the size of powder particles, dispersion ofthe powder becomes more difficult. Therefore, fine powder requires ahigh degree of dispersibility.

Existing solid phase methods or co-precipitation methods form acrystalline phase by high temperature calcination, therefore, requiringa high temperature calcining process and/or a grinding (orpulverization) process.

Due to the foregoing, synthesized perovskite powder entails problemssuch as poor morphology, broad particle size distribution, difficultiesin dispersibility caused by the agglomeration of particles due to heattreatment, the generation of microfine particles after pulverization,and the like.

In the case in which the perovskite powder is synthesized by ahydrothermal process without heat treatment, the dispersion problem maybe overcome. Moreover, hydrothermal synthesis may easily control themorphology of powder and enable the production of perovskite powder witha small particle size and a narrow distribution of particle sizes.

However, such a hydrothermal powder synthesis process has disadvantagesin that a crystal structure has an oxygen site substituted by hydroxyl(—OH) group, causing defects such as the formation of pores. Therefore,it is difficult to improve the crystallinity of synthesized particles.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a method of manufacturingperovskite powder in the form of microparticles with excellentcrystallinity and favorable dispersion, including preparation of a highconcentration and density metal oxide sol, as well as perovskite powderand a multilayer ceramic electronic component manufactured by the same.

According to an aspect of the present invention, there is provided amethod of manufacturing perovskite powder, the method including: washingmetal oxide hydrate to remove impurities therefrom; adding pure waterand an acid or a base to the metal oxide hydrate to prepare a metaloxide sol; and mixing the metal oxide sol with a metal salt to formperovskite particle cores (or nuclei); and conducting grain growth ofthe perovskite particle nuclei to produce perovskite powder.

The metal oxide sol may have a degree of transmittance of more than 50%.

The metal oxide sol may have a particle size of less than 10 nm.

The perovskite powder may be at least one selected from a groupconsisting of BaTiO₃, BaTi_(x)Zr_(1-x)O₃, Ba_(x)Y_(1-x)TiO₃,Ba_(x)Dy_(1-x)TiO₃ and Ba_(x)Ho_(1-x)TiO₃ (0<x<1).

The perovskite powder may have an average particle diameter ranging from40 to 200 nm and a crystal axial ratio (c/a) ranging from 1.0045 to1.0100.

The perovskite powder may have an average particle diameter ranging from40 to 60 nm and a crystal axial ratio (c/a) ranging from 1.0045 to1.0075.

The perovskite powder may have an average particle diameter ranging from60 to 80 nm and a crystal axial ratio (c/a) ranging from 1.0062 to1.009.

The perovskite powder may have an average particle diameter ranging from80 to 200 nm and a crystal axial ratio (c/a) ranging from 1.0080 to1.01.

The metal oxide hydrate may be at least one selected from a groupconsisting of titanium hydrate and zirconium hydrate.

The removal of the impurities may be performed by mixing metal oxidehydrate in a gel form with pure water and agitating a mixture toseparate the impurities from a metal portion, and removing a filtrate.

The acid used in the present invention may be at least one selected froma group consisting of hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, formic acid, acetic acid and polycarboxylic acid.

The base used in the present invention may be at least one selected froma group consisting of tetramethylammonium hydroxide andtetraethylammonium hydroxide.

The acid or the base may be added in an amount of 0.0001 to 0.2 molerelative to a content of metal oxide hydrate.

The preparation of the metal oxide sol may be performed by maintainingthe metal oxide hydrate at 0 to 60° C. for 0.1 to 72 hours whileagitating the same using a high viscosity agitator.

The metal salt used in the present invention may be barium hydroxide ora mixture of barium hydroxide and a rare-earth salt.

The perovskite particle nuclei may be formed at 60 to 150° C.

The perovskite powder may be formed while increasing a temperature ofthe perovskite particle nuclei from 150° C. to 400° C.

According to another aspect of the present invention, there is providedperovskite powder produced by: washing metal oxide hydrate to removeimpurities therefrom; adding pure water and an acid or a base to themetal oxide hydrate to prepare a metal oxide sol; mixing the metal oxidesol with a metal salt to form perovskite particle nuclei; conductinggrain growth of the perovskite particle nuclei to produce perovskitepowder as a final product.

According to a still further aspect of the present invention, there isprovided a multilayer ceramic electronic component including: a ceramicsintered body having laminated dielectric layers, each dielectric layercontaining perovskite powder; internal electrode layers formed on thedielectric layers; and external electrodes provided outwardly of theceramic sintered body and electrically connected to the internalelectrodes, wherein the perovskite powder is produced by: adding purewater and an acid or a base to metal oxide hydrate to prepare a metaloxide sol; mixing the metal oxide sol with a metal salt to formperovskite particle nuclei; and conducting grain growth of theperovskite particle nuclei.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a flowchart illustrating a process of manufacturing perovskitepowder according to an exemplary embodiment of the present invention;

FIG. 2 is a perspective view illustrating a multilayer ceramic capacitoraccording to an exemplary embodiment of the present invention;

FIG. 3 is a cross-sectional view taken along line A-A′ shown in FIG. 2;

FIGS. 4 through 10 are electron micrographs showing examples accordingto exemplary embodiments of the present invention and comparativeexamples; and

FIGS. 11A and 11B are TEM images showing examples according to exemplaryembodiments of the present invention and comparative examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings. However, other modifications,variations and/or alterations thereof may be possible and the presentinvention is not particularly limited to the following embodiments.These exemplary embodiments are provided to allow those skilled in theart to which the present invention pertains to more clearly understandthe present invention. Therefore, shapes and/or sizes of respectiveelements shown in the accompanying drawings may be enlarged for clarityand like reference numerals denote elements substantially having thesame configurations or performing similar functions and actionsthroughout the drawings.

In addition, unless explicitly described to the contrary, the word“comprise” and variations such as “comprises” or “comprising,” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements.

FIG. 1 is a flowchart illustrating a process of manufacturing perovskitepowder according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a method of manufacturing perovskite powderaccording to an exemplary embodiment of the present invention includes:washing metal oxide hydrate to remove impurities therefrom (S1); addingpure water and an acid or a base to the metal oxide hydrate to prepare ametal oxide sol (S2); mixing the metal oxide sol with a metal salt toform perovskite particle nuclei (S3); and conducting grain growth of theperovskite particle nuclei (S4) in order to produce perovskite powder asa final product (S5).

The following detailed description will be given to explain respectiveprocesses of the method of manufacturing perovskite powder according tothe foregoing exemplary embodiment.

Perovskite powder is a powder having ABO₃ structure and, in theexemplary embodiment of the present invention, metal oxide hydrate is asource of elements corresponding to B site while a metal salt is asource of elements corresponding to A site.

First, the metal oxide hydrate is washed to remove impurities therefromin operation S1.

The metal oxide hydrate may be at least one selected from a groupconsisting of titanium hydrate and zirconium hydrate.

Since titania and zirconia are very simply hydrolyzed, mixing thesematerials with pure water without alternative additives may precipitatetitanium hydrate and zirconium hydrate, respectively, in a gel state.

In order to remove impurities from the metal oxide hydrate by washingthe same, pure water is added to obtain a H₂O/metal molar ratio of morethan 10 while agitating the mixture from 10 minutes to 10 hours, so asto separate the impurities from a metal portion. Then, afterprecipitating the gel, the remaining filtrate is discarded.

More particularly, the metal oxide hydrate may be filtered underpressure to remove the residual solution, and further filtered whileadding pure water thereto in order to remove impurities present on asurface of particles.

Gas generated during agitation may be removed under vacuum or moreefficiently removed by introducing air under vacuum.

The metal oxide hydrate may be filtered under pressure to remove theresidual solution, and further filtered while adding pure water theretoto remove impurities present on a surface of particles.

Next, an acid or a base as well as pure water are added to the metaloxide hydrate in operation S2.

After filtering, the pure water is further added to the obtained metaloxide hydrate and the mixture is agitated using a high viscosityagitator while maintaining the same at a temperature of 0 to 60° C. for0.1 to 72 hours, thereby preparing a metal oxide hydrate slurry.

The acid or the base is added to the prepared slurry and, in this case,the acid or the base is used as a peptizing agent and may be added in anamount of 0.0001 to 0.2 mole relative to content of the metal oxidehydrate.

The acid used in the exemplary embodiment of the present invention isnot particularly limited but may include generally known acids, forexample, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid,formic acid, acetic acid, polycarboxylic acid, etc., which may be usedalone or in combination of two or more thereof.

The base used in the exemplary embodiment of the present invention isnot particularly limited but may include generally known bases, forexample, tetramethylammonium hydroxide, tetraethylammonium hydroxide,etc., which may be used alone or as a combination thereof.

According to the foregoing processes, a high concentration and puritymetal oxide sol may be prepared and, in this case, the metal oxide solmay have a transmittance of more than 50% and a particle size of lessthan 10 nm.

Following this, the metal oxide sol is mixed with a metal salt to formperovskite particle nuclei in operation S3.

The metal salt used herein may be barium hydroxide or a mixture ofbarium hydroxide and a rare-earth salt.

Such rare-earth salt is not particularly limited but may include, forexample, yttrium (Y), dysprosium (Dy), holmium (Ho), etc.

The formation of perovskite particle nuclei may be executed at 60 to150° C.

In this regard, a specific feature of the present invention is torapidly react the metal salt in dissolved state with the metal oxide solhaving high concentration and high purity.

In such a reaction, a mixing ratio of the reactant (metal salt/metaloxide) may range from 1 to 4, preferably 1.2 to 2.

In order to accelerate formation of perovskite particle nuclei, it ispreferable to increase a concentration and pH value of the mixtureincluding the metal oxide sol and the metal salt.

Then, the formed perovskite particle nuclei are subjected to graingrowth in operation S4, thereby producing perovskite powder as a finalproduct in operation S5.

Production of the perovskite powder may be conducted while increasing atemperature of the perovskite particle nuclei from 150 to 400° C.

Grain growth of particles may be slowly conducted at a high temperaturewhile decreasing the concentration and pH value of the foregoingmixture, in order to improve crystallinity.

Therefore, after the perovskite particle nuclei at reduced concentrationand pH value are placed in an autoclave and closely sealed, atemperature of the autoclave is increased from 150 to 400° C. and theparticle nuclei in the autoclave are maintained at this temperature for0.1 to 240 hours so as to proceed grain growth of particles.

According to the foregoing processes, highly crystalline perovskitepowder particles are obtained.

Such obtained perovskite powder particles may be at least one selectedfrom a group consisting of BaTiO₃, BaTi_(x)Zr_(1-x)O₃,Ba_(x)Y_(1-x)TiO₃, Ba_(x)Dy_(1-x)TiO₃ and Ba_(x)Ho_(1-x)TiO₃ (0<x<1).

The highly crystalline perovskite powder prepared by the method ofmanufacturing perovskite powder, as described above, may have an averageparticle diameter ranging from 40 to 200 nm and a crystal axial ratio(c/a) ranging from 1.0045 to 1.0100.

In particular, for a highly crystalline barium titanate powder having aparticle size of 40 to 60 nm, the crystal axial ratio (c/a) may rangefrom 1.0045 to 1.0075. Likewise, if the particle size ranges from 60 to80 nm, the crystal axial ratio may range from 1.0062 to 1.0090. Also,when the particle size ranges from 80 to 200 nm, the crystal axial ratiomay range from 1.0080 to 1.01.

Three axial axes are defined as ‘a’, ‘b’ and ‘c’ and b-axis in atetragonal particle has substantially the same length as of a-axis, thusbeing indicated as ‘a-axis.’ In this regard, the crystal axial ratio(c/a) means a ratio of lattice lengths of c-axis to a-axis.

FIG. 2 is a perspective view illustrating a multilayer ceramic capacitoraccording to an exemplary embodiment of the present invention while FIG.3 is a cross-sectional view taken along lines A-A′ shown in FIG. 2.

In the present exemplary embodiment, the following detailed descriptionwill be given to explain a multilayer ceramic capacitor selected as anillustrative example among various multilayer ceramic electroniccomponents.

A multilayer ceramic capacitor 100 according to this exemplaryembodiment includes: a ceramic sintered body 110 having a plurality ofdielectric layers 111 laminated one after another; internal electrodelayers 130 a and 130 b formed on the laminated dielectric layers 111;and external electrodes 120 a and 120 b provided on outer surfaces ofthe ceramic sintered body 110 and electrically connected to the internalelectrodes.

The dielectric layers 111 of the multilayer ceramic capacitor 100 mayinclude perovskite powder produced according to an exemplary embodimentof the present invention.

A method of manufacturing the foregoing perovskite powder andcharacteristics thereof have been described in detail above.

The multilayer ceramic capacitor 100 according to the present exemplaryembodiment shows high dielectric constant and excellent reliability.

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the following examples and comparativeexamples. However, the present invention is not particularly limitedthereto.

Example 1 Preparation of Titania Nano Sol Using Acidic Peptizing Agentand Titanium Alkoxide

More than 5-fold volume of pure water was added to titanium isopropoxideand the mixture was hydrolyzed under agitation. After precipitating atitanium hydrate gel formed by hydrolysis, a supernatant was discardedand 10-fold weight of pure water was further added to the titaniumhydrate gel. Then, the gel was washed under vacuum while agitating thesame. In order to remove an organic material formed during washing, theforegoing procedures are repeated twice. A second supernatant wasdiscarded again and a precipitate was passed through a filter paper.Then, pure water was added again to the obtained titanium hydrate inorder to reach a molar concentration of 5M, followed by adding nitricacid to satisfy H+/Ti=0.5. The mixture was subjected to peptization for3 hours by increasing a temperature of the mixture in an extent of about50° C. while agitating the same using a high viscosity agitator, therebypreparing a metal oxide sol. The metal oxide sol formed by peptizationwas a translucent, slightly bluish and mono-dispersed sol with excellentstability. As a result of measuring a transmittance of the formed sol byTurbiscan, the transmittance of the sol was found to be about 75%. Forreference, pure water has a transmittance of 90%. TiO₂ particles have aparticle size of about 3 nm, are formed in anatase grade andmono-crystalline state.

Example 2 Preparation of Titania Nano Sol Using Acidic Peptizing Agentand Titanium Salt

More than 5-fold volume of pure water was gently added to titanium oxidedichloride (TiOCl₂) under agitation, thus preparing a transparentsolution. Ammonia water was slowly added to the solution to increase pHvalue, thus inducing gel reaction. Continuously adding ammonia water,the gel was dissolved to generate a precipitate containing titaniumhydrate. While precipitating the formed titanium hydrate, a supernatantwas discarded and 10-fold weight of pure water was added again to atitanium hydrate gel (that is, the precipitate). The mixture was washedunder vacuum while agitating. These procedures are repeated six times. Apeptizing process is conducted by the same procedures as described inExample 1. The prepared TiO₂ sol exhibited a transmittance of 70%.

Example 3 Preparation of Titania Nano Sol Using Alkaline Peptizing Agentand Titanium Alkoxide

More than 5-fold volume of pure water was gently added to titaniumisopropoxide under agitation to conduct hydrolysis. After precipitatinga titanium hydrate gel formed by hydrolysis, a supernatant was discardedand 10-fold weight of pure water was added again to the titanium hydrategel. The mixture was washed under vacuum while agitating. In order toremove an organic material formed during washing, the foregoingprocedures are repeated twice. A second supernatant was discarded againwhile a precipitate was passed through a filter paper. Then, pure waterwas added again to the obtained titanium hydrate in order to reach amolar concentration of 5M, followed by adding tetraethyl ammoniumhydroxide to satisfy OH−/Ti=0.1. The mixture was subjected topeptization for 6 hours by increasing a temperature of the mixture in anextent of about 60° C. while agitating the same using a high viscosityagitator, thereby preparing a metal oxide sol. Such formed metal oxidesol was a translucent, slightly bluish and mono-dispersed sol withexcellent stability. The TiO₂ sol showed a transmittance of 65%.

Comparative Example 1 Preparation of Titania Nano Sol Using AcidicPeptizing Agent and Titanium Alkoxide

The same procedures as described in Example 1 were used, except that anorganic material such as IPA formed after hydrolysis performed by mixingtitanium isopropoxide with pure water was not washed out, instead, beingagitated for 48 hours then subjected to peptization under the sameconditions as described in Example 1. As a result, although anatase TiO₂sol was obtained, a transmittance thereof was not more than 5%.

Comparative Example 2 Preparation of Titania Nano Sol Using AcidicPeptizing Agent and Titanium Alkoxide

The same procedures described in Example 1 were used, except that anorganic material such as IPA formed after hydrolysis performed by mixingtitanium isopropoxide with pure water was not washed out, instead, beingagitated for 48 hours. Then the mixture was subjected to peptizationunder the same conditions as described in Example 1, except that nitricacid was added to titanium hydrate to satisfy H+/Ti=0.2. As a result,although anatase TiO₂ sol was obtained, a transmittance thereof was notmore than 30%.

The following Table 1 shows synthesis conditions described in Examples 1to 3 and Comparative Examples 1 and 2, and assessment results thereof.

TABLE 1 Synthesis conditions Content of Assessment results Washingpeptizing Average during Peptizing agent (H+ Transmittance particle Tisource hydrolysis agent or OH−/Ti) (%) size (nm) Ex. 1 Titanium ∘ Nitricacid 0.05 75 7 isopropoxide Ex. 2 Titanium ∘ Nitric acid 0.05 70 6 oxidedichloride Ex. 3 Titanium ∘ Tetraethyl 0.1 65 8 isopropoxide ammoniumhydroxide Com. Titanium x Nitric acid 0.05 5 12 Ex. 1 isopropoxide Com.Titanium x Nitric acid 0.2 30 7 Ex. 2 isopropoxide

Example 4 Synthesis of Barium Titanate

Barium hydroxide hydrate (Ba(OH)₂8H₂O) was entered into a reactor,followed by nitrogen purging and agitating at 100° C. to prepare a metalsalt. This metal salt was added to the TiO₂ sol having a transmittanceof 75% and satisfying H+/Ti=0.5, which was prepared according to theprocedures in Example 1. The mixture was rapidly admixed whileincreasing the temperature of the sol to 100° C. The mixture was closelysealed and agitated at 100° C. to conduct reaction. After 30 minutes,the raw material was completely converted into barium titanate, in turnterminating a primary reaction. Next, pure water was added to theproduct in order to decrease a concentration of the product, that is,barium titanate, followed by grain growth of the barium titanate for 20hours after increasing the temperature to 250° C. After filtering, thegrown particles were washed using pure water and dried to yield powderwith BET-specific surface area of 14.68 m²/g, a particle diameter of 64nm when measured using SEM, D99/D50 ratio (particle size of 99%particles/particle size of 50% particles) of 1.51 that indicatesrelatively uniform particle size distribution, a spherical morphology,and a crystal axial ratio (c/a) of 1.0069 that demonstrates excellentcrystallinity in spite of a small particle size. The particles hadinternal pores of about 8 ppm in volume fraction.

Example 5 Synthesis of Barium Titanate

Substantially the same procedures as described in Example 4 were used,except that a concentration at grain growth of particles was increasedand a processing time was extended to increase a size of the particles.The synthesized powder had BET-specific surface area of 13.00 m²/g, aparticle diameter of 75 nm when measured using SEM, D99/D50 ratio of1.54 that indicates relatively uniform particle size distribution, aspherical morphology, and a crystal axial ratio (c/a) of 1.0082 thatdemonstrates excellent crystallinity in spite of a small particle size.

Example 6 Synthesis of Barium Titanate

Substantially the same procedures as described in Example 4 were used,except that a temperature of 330° C. was maintained for 30 hours duringsecondary reaction for securing grain growth of particles. Thesynthesized powder had BET-specific surface area of 14.36 m²/g, aparticle diameter of 62 nm when measured using SEM, D99/D50 ratio of1.62, a spherical morphology, and a crystal axial ratio (c/a) of 1.0078that demonstrates excellent crystallinity in spite of a small particlesize.

Example 7 Synthesis of Barium Titanate

Barium hydroxide hydrate (Ba(OH)₂8H₂O) was entered into a reactor,followed by nitrogen purging and agitating at 100° C. to prepare a metalsalt. This metal salt was added to the TiO₂ sol having a transmittanceof 65% and satisfying OH−/Ti=0.1, which was prepared according to theprocedures in Example 3. The mixture was rapidly admixed whileincreasing the temperature of the sol to 100° C. The mixture was closelysealed and agitated at 100° C. to conduct reaction. After 30 minutes,the raw material was completely converted into barium titanate, in turnterminating a primary reaction. Next, pure water was added to theproduct in order to decrease a concentration of the product, that is,barium titanate, followed by grain growth thereof for 20 hours afterincreasing the temperature to 250° C. If using a basic TiO₂ sol, agrain-growth rate may increase because of higher pH. The produced powderhad BET-specific surface area of 9.32 m²/g, a particle diameter of 99 nmwhen measured using SEM, D99/D50 ratio of 1.65, a spherical morphology,and a crystal axial ratio (c/a) of 1.0094. The particles had internalpores of about 29 ppm in volume fraction, which were slightly increasedowing to increase in grain-growth rate.

Comparative Example 3 Synthesis of Barium Titanate

Barium titanate was synthesized under substantially the same conditionsas described in Example 4, except that TiO₂ sol having a transmittanceof 5% prepared according to the procedures in Comparative Example 1 wasused as a raw material. The dried powder had BET-specific surface areaof 8.89 m²/g, a particle diameter of 88 nm when measured using SEM,D99/D50 ratio of 2.2, a slightly angular morphology, and a crystal axialratio (c/a) of 1.0075. When using TiO₂ sol with a large particle sizeand poor dispersion as a raw material, extremely non-uniform particleswere obtained and, due to a high grain-growth rate thereof, theparticles had a large amount of internal pores of 8320 ppm. As a result,the particles showed poor crystallinity, as compared with particle size.

Comparative Example 4 Synthesis of Barium Titanate

Barium titanate was synthesized under substantially the same conditionsas described in Example 4, except that TiO₂ sol prepared by adding apeptizing agent in large amount during peptization (H+/Ti=0.2) whilewashing according to the procedures in Example 4 after hydrolysis wasused as a raw material. Such TiO₂ sol had a favorable transmittance of70%. The synthesized powder had BET-specific surface area of 14.9 m²/g,a particle diameter of 65 nm when measured using SEM, D99/D50 ratio of1.7, and a spherical and relatively uniform particle shape. However, acrystal axial ratio (c/a) of the powder was 1.0061, which is low, ascompared with particle size. Although the particles had a small amountof internal pores of 35 ppm, crystallinity of the particles was not soexcellent.

Comparative Example 5 Synthesis of Barium Titanate

Barium titanate was synthesized under substantially the same conditionsas described in Example 4, except that mixing raw materials was startedat 30° C. The synthesized powder had BET-specific surface area of 13.76m²/g, a particle diameter of 69 nm, D99/D50 ratio of 1.8, and aspherical and relatively uniform particle shape. However, the particleshad a large amount of internal pores of 21074 ppm, and therefore, showeda relatively low crystal axial ratio (c/a) of 1.0056.

Comparative Example 6 Synthesis of Barium Titanate

Barium titanate was synthesized under substantially the same conditionsas described in Example 4, except that reaction was carried out at 250°C. for 20 hours by increasing a temperature immediately after admixingraw materials, instead of performing primary and secondary synthesesseparately. The synthesized powder had BET-specific surface area of 8.3m²/g, a particle diameter of 108 nm, D99/D50 ratio of 2.5 whichindicates considerably non-uniform particle size distribution, and acrystal axial ratio of 1.0094. If two-step reaction is not used,uniformity of particles becomes significantly worse althoughcrystallinity is not considerably deteriorated.

Comparative Example 7 Synthesis of Barium Titanate Using HydrothermalProcess and Calcinations

Primary synthesis was conducted under substantially the same conditionsas described in Example 4. After completing the primary synthesis,barium titanate powder was produced by decreasing a temperature,filtering a solution and washing the same. Here, the formed bariumtitanate powder had a spherical morphology and a particle size of about10 nm with uniform particle size distribution, and each particle had acubic shape. Such particles were heated at 900° C. for 3 hours toconduct grain growth. The synthesized powder had BET-specific surfacearea of 5.8 m²/g, a particle diameter of 96 nm when measured using SEM,D99/D50 ratio of 2.23 and non-uniform morphology, and showed numerousinterparticle necks. A crystal axial ratio (c/a) of the particles was1.0069, which is considerably low, as compared with particle size.

The following Table 2 shows synthesis conditions described in Examples 4to 7 and Comparative Example 3 to 7, and assessment results thereof.

TABLE 2 Reaction conditions Assessment results TiO₂ sol XRD Molar Step 1Step 2 BET Lattice TEM ratio of Temp. Time of Temp. Specific SEMconstant Pore peptizing Feed of Step 1 of surface D50 D99/ ratio Volumetransmittance agent process temperature Step 1 (min) Step 2 time area(nm) D50 (c/a) (ppm) Ex. 4 75% 0.05 Two steps 100° C. 100° C. 30 250 2014.68 63.6 1.51 1.0069 8 Ex. 5 75% 0.05 Two steps 100° C. 100° C. 30 25035 13.00 74.77 1.54 1.0082 12 Ex. 6 75% 0.05 Two steps 100° C. 100° C.30 330 30 14.36 61.5 1.62 1.0078 2 Ex. 7 65% 0.1 Two steps 100° C. 100°C. 30 250 20 9.32 99.4 1.65 1.0094 29 Com.  5% 0.05 Two steps 100° C.100° C. 30 250 20 8.89 87.7 2.21 1.0075 8320 Ex. 3 Com. 70% 0.2 Twosteps 100° C. 100° C. 30 250 20 14.9 65 1.7 1.0061 35 Ex. 4 Com. 75%0.05 Two steps  30° C. 100° C. 30 250 20 13.76 68.7 1.80 1.0056 21074Ex. 5 Com. 75% 0.05 One step 100° C. — — 250 20 8.268 107.9 2.48 1.00944700 Ex. 6 Com. 75% 0.05 Calcination 100° C. 100° C. 30 900 3 5.8 95.62.23 1.0069 20804 Ex. 7 after one step

Example 8 Synthesis of Ba_(0.98)Y_(0.02)TiO₃ Using Hydrothermal Process

Barium hydroxide octahydrate (Ba(OH)₂8H₂O) and yttrium acetate hydratewere entered at a molar ratio of 98:2 into a reactor, followed bynitrogen purging and agitating at 80° C. to prepare a metal salt. Thismetal salt was added to the TiO₂ sol prepared according to the foregoingprocedures. The mixture was closely sealed and agitated at 130° C. toconduct reaction. After 10 minutes, the raw materials were completelyconverted into barium titanate, in turn terminating nucleus formation.After decreasing the temperature and replacing the formed gas withnitrogen, pure water was added to decrease a concentration of bariumtitanate. Here, this solution was maintained at a pH value of 12.3.After increasing the temperature to 250° C., the barium titanate wassubjected to grain growth for 20 hours. After filtering, washing withpure water and drying, the obtained powder had BET-specific surface areaof 10.6 m²/g, a particle diameter of 85 nm when measured using SEM.

FIGS. 4 to 10 are electron micrographs showing examples according toexemplary embodiments of the present invention and comparative examples.

FIGS. 11A and 11B are transmission electron microscope (TEM) photographsshowing examples according to exemplary embodiments of the presentinvention and comparative examples.

More particularly, FIG. 4 is an electron micrograph showing bariumtitanate particles obtained in Example 4. Likewise, FIGS. 5, 6 and 7 areelectron micrographs showing barium titanate particles obtained inExamples 5, 7 and 8, respectively.

Similarly, FIGS. 8, 9 and 10 are electron micrographs showing bariumtitanate particles obtained Comparative Examples 3, 5 and 6,respectively.

FIG. 11A is a TEM photograph showing barium titanate particles obtainedin Example 7 while FIG. 11B is a TEM photograph showing barium titanateparticles obtained in Comparative Example 7.

Referring to FIGS. 4 to 10, 11A and 11B, it can be seen that perovskitepowder prepared according to an exemplary embodiment of the presentinvention includes particles with a small amount of pores and hasexcellent crystallinity. In addition, since the present inventionrequires no alternative calcination and/or pulverization processes, thesynthesized powder does not contain a lot of fine powder, and dispersionthereof is very easily conducted.

Moreover, the production process according to an exemplary embodiment ofthe present invention has advantages such as reduced raw material costs,which in turn reduce overall production costs.

A multilayer ceramic electronic component fabricated according to anexemplary embodiment may have beneficial features such as thepreparation of pervoskite powder without large particles, simpledispersibility properties sufficient to easily embody a reduction oflayer thickness, a high dielectric constant and excellent reliability,and so forth.

As set forth above, according to exemplary embodiments of the presentinvention, a high concentration and purity metal oxide sol is preparedthrough peptization and used to synthesize perovskite powder, therebymanufacturing high crystallinity perovskite powder without calcinationand pulverization. The present invention also has advantages such asdecreased generation of fine powder, good dispersion, and the like.

Furthermore, the pervoskite powder shows excellent effects such asdecreased generation of pores.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is: 1-18. (canceled)
 19. A multilayer ceramic electroniccomponent including: a ceramic sintered body having laminated dielectriclayers, each dielectric layer containing perovskite powder; internalelectrode layers formed on the dielectric layers; and externalelectrodes provided outwardly of the ceramic sintered body andelectrically connected to the internal electrodes, wherein theperovskite powder is produced by: adding pure water and an acid or abase to metal oxide hydrate to prepare a metal oxide sol; mixing themetal oxide sol with a metal salt to form perovskite particle nuclei;and conducting grain growth of the perovskite particle nuclei.
 20. Themultilayer ceramic electronic component of claim 19, wherein theperovskite powder is at least one selected from a group consisting ofBaTiO₃, BaTi_(x)Zr_(1-x)O₃, Ba_(x)Y_(1-x)TiO₃, Ba_(x)Dy_(1-x)TiO₃ andBa_(x)Ho_(1-x)TiO₃ (0<x<1).
 21. The multilayer ceramic electroniccomponent of claim 19, wherein the perovskite powder has an averageparticle diameter ranging from 40 to 200 nm and a crystal axial ratio(c/a) ranging from 1.0045 to 1.0100.
 22. The multilayer ceramicelectronic component of claim 19, wherein the perovskite powder has anaverage particle diameter ranging from 40 to 60 nm and a crystal axialratio (c/a) ranging from 1.0045 to 1.0075.
 23. The multilayer ceramicelectronic component of claim 19, wherein the perovskite powder has anaverage particle diameter ranging from 60 to 80 nm and a crystal axialratio (c/a) ranging from 1.0062 to 1.009.
 24. The multilayer ceramicelectronic component of claim 19, wherein the perovskite powder has anaverage particle diameter ranging from 80 to 200 nm and a crystal axialratio (c/a) ranging from 1.0080 to 1.01.